In mammals, the mobilization of arachidonic acid from the sn2 ester bond of phospholipids is greatly due to the activation of cytosolic phospholipase A2 (cPLA2) following the receptor activation induced by a number of agonists including hormones, neurotransmitters, neuropeptides and growth factors.
Considering the mechanism of PLA2 activation via the agonist-receptor interaction, the G-proteins have been proposed to mediate the receptor induced activation through two distinct mechanisms: (i) direct interaction with the PLA2, since it is well known that the treatment with pertussis toxin reduces its enzymatic activity; or (ii) indirectly mediated through phospholipase C (PLC) activation, phosphorilation and activation of the PLA2 by the Mitogen Activated Protein Kinases (MAPK).
Two isoforms of the phospholipase A2 have been identified in mammals, a 14 kDa secretory form and a 85 kDa cytosolic form (cPLA2) which do not share amino acid sequence homology and differ in their catalytic and regulatory mechanisms. The cytosolic phospholipase A2 is located in the cytosol of quiescent cells, for example platelets and leucocytes: lipopolisaccharide, thrombin or cytokines (for example Interleukin 1β), Tumor Necrosis Factor α, but also neuropeptides such as tachikinins, bradikinins or neurotransmitters such as purines, particularly ATP, and serotoninergic, adrenergic and muscarinic agonists activate the enzyme leading to an increase of the intracellular calcium levels and a rapid phosphorilation of the enzyme by protein Kinase C and a subsequent translocation to the plasma membrane where it binds to the phospholipid substrate. These mediators also induce the de novo synthesis of the enzyme (E. Armandi-Burgermeister, U. Tibes, B. M. Kaiser, W. G. Friebe, W. V. Scheuer, “Suppression of cytokine synthesis, integrin expression and chronic inflammation by inhibitors of cytosolic phospholipase A2” Europ. J. Pharmacol., 326 (1997) 237-250).
The tight intermodulation of the G protein, PKC, cPLA2 systems and the involvement of the cPLA2 in the production of lipid and lysolipid mediators (Glycerophosphoinositol-4-phosphate in intracellular signaling “C. P. Berrie, M. Falasca, A. Carvelli, C. Iurisci and D. Corda, in Bioactive Lipids, Vanderbock YY/ed. Plenum Publishing Corporation New York, 1998) make the PLA2 a potentially important pharmacological target.
The applicant has now originally found that a substance generated concomitantly with the release of arachidonic acid, that is L-α-glycero-phospho-D-mio-inositol (GPI), is an autacoid and, furthermore, its potassium, calcium and zinc salts and other new derivatives and analogues obtained by chemical semisynthesis and having the general formula (I) subsequently described, exert a potent inhibitory effect on the release of arachidonic acid via a negative modulation of the PLA2 in vitro activation and can be effectively used for the treatment of pathologies mediated by the activation of PLA2 as following described.